1. Field of the Invention
This invention relates to the art of operating cells that are used for the electrolysis of brine to produce chlorine and caustic, and in particular to such cells wherein a diaphragm divides the cell into anolyte and catholyte portions, with the diaphragm being of relatively hydrophobic material such as highly crystalline polytetrafluoroethylene. It concerns a method of re-wetting the diaphragm so that flow therethrough may be re-established at a desired greater value.
2. Description of the Prior Art
The operation of diaphragm-type electrolytic cells to produce caustic and chlorine is well known to those skilled in the art. Though it has been usual to use asbestos for the diaphragms of such cells, there has recently been a trend to change to different diaphragm materials, such as crystalline polytetrafluoroethylene, because of the considerable occupational-hazard problems encountered in the manufacture of asbestos and the expense of meeting them. The crystalline polytetrafluoroethylene material is quite satisfactory as a diaphragm material, except for its drawback of being rather hydrophobic and consequently tending to dewet while in service. When the diaphragm dewets, flow of material through the diaphragm slows down greatly or even substantially stops. It has often been necessary to halt the electrolysis operation when this happens and possibly also disassemble the cell in order to take appropriate steps to bring the diaphragm back into service.
In the operation of a diaphragm cell, the efficiency of the entire operation is importantly affected by the flow of liquid through the diaphragm. The brine can be supplied to the anolyte chamber only at a rate such that, considering the flow through the diaphragm, the level in the anolyte chamber remains at a tolerable level. It is usual for a diaphragm to begin to be somewhat slow in passing liquid after some days or weeks of service. Diaphragms of polytetrafluoroethylene sometimes pass liquid too slowly even at the start-up of an electrolysis operation because they have become partially dewetted before the electrolysis begins.
Many wetting agents are known, but most of them are not at all satisfactory for use in connection with a cell for the electrolysis of brine to produce caustic and chlorine. The usual nonionic wetting agents (ones of the propylene oxide-ethylene oxide type) are substantially unstable or insoluble in alkaline media.